UUID Generator and Checker
Text & Dev ToolsRandom v4 or sortable v7 UUIDs in bulk, and a checker that reads any UUID's version and timestamp.
What you type never leaves this device. Everything here runs in your browser — your text is never uploaded, stored or seen by us. Open your network tab and check.
Generating…
How this is calculated
A UUID is 128 bits, written as 32 hexadecimal digits: 8-4-4-4-12.
Version 4 xxxxxxxx-xxxx-4xxx-Vxxx-xxxxxxxxxxxx
122 random bits
Version 7 tttttttt-tttt-7ccc-Vxxx-xxxxxxxxxxxx
t = Unix time in milliseconds (48 bits)
c = counter, so ones made in the same millisecond stay in order
x = random
V is 8, 9, a or b — the variant bits RFC 9562 fixes.How it works
A UUID — a universally unique identifier, which Microsoft calls a GUID — is a 128-bit number made so that two systems can each create IDs without asking each other and still never clash. The standard is RFC 9562, published in 2024 to replace RFC 4122. Six of the 128 bits are fixed: four say which version the UUID is, and two mark it as the RFC's variant. That is why every version 4 UUID has a 4 as the first digit of its third group, and an 8, 9, a or b as the first of the fourth.
Version 4 fills the other 122 bits at random. There are so many possible values that you would need to generate about 2.7 quintillion (2.7 × 10¹⁸) of them before there was even a 50% chance that two matched. That only holds if the randomness is good, which is why this page draws it from your browser's cryptographically secure generator, crypto.getRandomValues, as RFC 9562 recommends, and never from Math.random.
Version 7 puts the current time, in milliseconds since 1970, in the first 48 bits, so UUIDs sort in the order they were made — as text or as raw bytes. That matters in databases: RFC 9562 notes that random keys scatter new rows across an index, while time-ordered keys land near each other, and that the difference can be an order of magnitude or more. Here the 12 bits after the version are a counter, started at a random value each millisecond and counted up within it, so a batch made in one millisecond still comes out in order.
The checker reads any UUID you paste: whether it is valid, its version and variant, and for version 7, the moment it was made. It accepts upper or lower case, braces, a urn:uuid: prefix, and the 32 digits without hyphens.
Worked example
Reading the version 7 example from RFC 9562: 017f22e2-79b0-7cc3-98c4-dc0c0c07398f
- First 12 digits 017f22e279b0 = 1,645,557,742,000 milliseconds after 1 January 1970
- = 22 February 2022, 19:22:22 UTC (2:22:22 PM in New York)
- Next digit 7 → version 7
- First of 4th group 9 → binary 1001, starts 10 → the RFC 9562 variant
- Everything else counter and random bits
Made on 22 February 2022 at 19:22:22 UTC, and it will sort after every UUID made earlier
How to use it
- Choose Version 4 for a plain random ID, or Version 7 for IDs that sort by the time they were made, such as database keys.
- Set how many you need, from 1 to 1,000.
- Tick the format your system expects: upper case, without hyphens, or in curly braces.
- Copy one, or copy all of them, one per line. Generate new draws a fresh set.
- To read an existing UUID, choose Check a UUID and paste it.
What this tool does not do
- Generates versions 4 and 7 only. The checker recognises every version, but the older time-based versions 1 and 6 and the name-based versions 3 and 5 are not generated.
- A version 7 UUID reveals when it was made, to the millisecond. RFC 9562 advises version 4 wherever a UUID is used for anything security-related.
- UUIDs are identifiers, not secrets. Do not use one as a password or an access token.
- Version 7 order is only as good as the clock of the device making them. UUIDs made on different machines interleave by each machine's own time.
- Batches are limited to 1,000 at a time.
Frequently asked questions
What is the difference between a UUID and a GUID?
Nothing that matters in text. GUID is Microsoft's name for the same 128-bit format, and Microsoft tools often write it upper-case inside curly braces, which the format options here reproduce.
Can two UUIDs ever be the same?
In principle, yes; in practice, not if they are made properly. A version 4 UUID has 122 random bits, so about 2.7 quintillion would have to be generated before a duplicate became as likely as not. Duplicates in the real world come from broken random number generators or copied values, not from chance.
Should I use version 4 or version 7?
Version 7 for database primary keys and anything you want sorted by creation time, because new keys sit next to each other in the index instead of being scattered through it. Version 4 when the ID should reveal nothing, including when it was made — RFC 9562 recommends version 4 for anything security-related.
Is a UUID random enough to use as a secret token?
No. UUIDs are designed to be unique, not secret, and they often end up in URLs, logs and databases. Version 7 also gives away its creation time. For a password or an access token, use a generator made for that, such as the password generator on this site.
Upper case or lower case?
Either. RFC 9562 treats the hexadecimal digits as case-insensitive, so 017F22E2-… and 017f22e2-… are the same UUID. Lower case is the more common convention; some Microsoft tools write upper case.
Are the UUIDs generated on a server?
No. They are made in your browser, with its cryptographically secure random number generator, and never sent anywhere. The only requests the page makes once you use it are small ones recording that the tool was used.
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Last updated 13 September 2026.